Stratum corneum of a skin has the function of cutaneous barrier, thereby suppressing evaporation of water from the body and protecting the body from the exterior stimuli. This barrier function is easily damaged by UV, surfactant, dryness, mechanical stimulation, activated oxygen, residual chlorine in tap water and the like, and such damage in the skin barrier is known to induce dry skin, atopic dermatitis, rough skin and the like.
Various means that improve such a barrier function have been reported. Among these means, there are methods to be carried out by the external administration of a plant extract such as Arnica or turmeric (JP-A-2003-171310), and the external administration of polysaccharides such as pamaquine and pachymaran (JP-A-2002-275046).
The stratum corneum of mammalian (including human) skin is also known to contain a considerable level of ceramides consist of fatty acids and sphingoid bases and these substances are thought to have the function of preventing evaporation of water from the body. Attempts have also been made to improve the water holding function of the stratum corneum by administering such ceramide and sphingosine.
JP-A-1994-271446 discloses effectiveness of the application on the skin of sphingosines in reducing wrinkles controlling.
However, systemic application of such an external medication is difficult to continue for consecutive days, and also could induce inflammation, stimulus, allergic reaction and the like. In the meantime, systemic application can be readily achieved if the medication is administered by oral ingestion.
For example, Fragrance Journal, 23(1), 81(1995) describes enhancement of water holding function of the skin by oral ingestion of the ceramide, and JP-A-1999-113530 describes skin treatment and cosmetic effects realized by the oral ingestion of the ceramide. JP-A-2003-2835 describes that the absorption is improved when the sphingoglycolipid is ingested with a plant sterol, and such improvement is manifested by increase in the water holding capacity of the stratum corneum as well as amelioration of the skin roughness. However, oral ingestion of the components as mentioned above has so far failed to show sufficient water holding and barrier function of the skin.
With regard to the diacylglycerol, JP-A-1992-300825 discloses its function of suppressing the increase of the neutral fat in blood, and JP-A-2001-64170 discloses its function of increasing blood HDL cholesterol. Accordingly, diacylglycerols are used in cooking oils and various other food products produced by using oil or a fat.
In spite of the situation as described above, no food has so far been known that contain both the diacylglycerol and the glycosylated ceramide. Effectiveness of oral ingestion of sphingolipids in improving the barrier function and the water holding function remains to be unknown, and so does oral ingestion of sphingolipids.